In a separate pot, cook the guajillo and ancho chiles until they are fully softened and hydrated.

Remove the head of garlic used to cook the beef and place it in a blender. Remove the stems and seeds from the chiles, then add them to the blender as well. Add some of the cooking broth and blend until smooth.

Once the chile mixture is smooth, strain it for a finer texture. Add it back to the pot with the beef broth, then add the shredded beef and coriander seeds. Bring to a boil and simmer for 10 to 15 minutes so the beef absorbs the flavors.

Serve with chopped onion and cilantro, and with chile de árbol salsa if you like.